1. Field of the Invention
The present invention relates to solid state microwave amplifiers and, in particular, to a bi-directional amplifier module that incorporates spatial combiners and solid state amplifiers.
2. Related Art
High-power amplifiers are a necessary component of most RF transmission systems at microwave and millimeter wave frequencies. Currently, most systems that require high power (greater than approximately 50 Watts) use traveling wave tube (TWT) amplifiers. TWT amplifiers may have output power in the kilowatt range, but such amplifiers also have large noise figures and require high-voltage power supplies. In addition, TWTs are typically very large, expensive and unreliable. Solid state amplifiers, on the other hand, have a lower noise figure and use a low-voltage power supply. As compared to TWT amplifiers, solid state amplifiers are smaller, lighter, more reliable, easier to manufacture and less expensive. For the foregoing reasons, solid state amplifiers are generally more desirable than TWT amplifiers. However solid state amplifiers have a limited output power (less than approximately 10 Watts) making them unsuitable for some microwave applications.
The power from many individual solid state amplifiers or microwave integrated circuits (MICs) can be coherently added or combined to increase the overall output power. A conventional power combining circuit for increasing overall output power is a corporate combiner. In a corporate combiner, an input signal is split into N stages to form 2N separate microstrip lines. Unfortunately, a corporate combiner generally has insertion losses and resistive losses along with phase coherency problems in the 2N channels that significantly impact corporate combiner efficiency, particularly when it has a large number of stages. Indeed, the efficiency for a large number of stages is low. However, corporate converters are useful in many applications and will continue to be utilized for supporting specific microwave systems.
Other types of MIC combiners utilize spatial arrangement techniques, such as spatial power splitting and combining. The term spatial power splitting and combining generally refers to the placement of multiple microstrip transitions within a waveguide, coaxial cable or other microwave channel in order to capture and split propagating electromagnetic energy and transfer such energy onto multiple microstrip transmission lines as electrical signals. The electrical signals on the microstrip transmission lines are amplified by solid state amplifiers, and the outputs of these amplifiers are coherently combined via microstrip-to-waveguide converters and inserted or re-launched as amplified electromagnetic energy into a waveguide. The resulting amplified microwave signal may then be coupled, via the waveguide, to a radar antenna, a communications antenna, a transceiver, or other device. The design trade-offs between a spatial combiner and a corporate combiner are discussed at length in current literature and are generally well-known by those skilled in the art.
Currently, when a bi-directional exchange of microwave signals is desired, a two-way link is constructed using two separate modules and microwave channels. A first transmitter and receiver pair use a first channel, such as a waveguide, for sending microwave signals in one direction, and a second transmitter and receiver pair use a second channel for transmission in the other direction. Amplification is provided using conventional amplifiers, such as TWTs, corporate converters with MICs, or spatial converters with MICs.
In general the present invention pertains to a system and method for providing bi-directional amplification of microwave signals via a bi-directional amplifier module that can be coupled to a microwave channel, such as a waveguide or coaxial cable. Utilization of such a bi-directional amplifier module helps to reduce space requirements and cost for various applications, such as microwave communications and radar, for example.
A bi-directional amplifier module in accordance with an exemplary embodiment of the present invention is illuminated by a downstream illumination source and an upstream illumination source. The illumination sources are coupled to separate ends of an array amplifier modules having waveguide to microstrip converters that provide for upstream and downstream energy flow. Switchable amplifiers provide for amplification in both directions, and the converters coherently combine the output of the amplifiers to provide increased power to the electromagnetic signal entering the waveguide.
The present invention may also be viewed as a bi-directional amplification method. A method in accordance with an exemplary embodiment of the present invention can be broadly conceptualized by the following steps: illuminating an array of upstream converters and downstream converters; converting the illuminations to downstream electrical signals and upstream electrical signals for transmission on microstrip transmission lines; receiving the downstream electrical signals at downstream amplifiers; combining downstream amplified signals at the upstream converter for downstream illumination; receiving the upstream electrical signals at upstream amplifiers; and combining upstream amplified signals at the downstream converter for upstream illumination.